Tornadoes in the USA are concentrating on fewer days, but their power dissipation is not
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ORIGINAL PAPER
Tornadoes in the USA are concentrating on fewer days, but their power dissipation is not Todd W. Moore 1
&
Tyler Fricker 2
Received: 6 December 2019 / Accepted: 17 September 2020 / Published online: 26 September 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract The Gini coefficient, Palma ratio, and the ratio of the percentage of tornadoes occurring on days with 20+ tornadoes to the percentage of tornadoes occurring on days with 1–9 tornadoes were used to measure the concentration of tornadoes in the USA for each year over the period 1954–2017. The Gini coefficient and Palma ratio were also used to measure the concentration of tornado power. All three metrics illustrate that most tornadoes are concentrated on relatively few days and that power is even more concentrated. Trend tests illustrate that tornadoes are becoming more concentrated over time, but the power dissipated by tornadoes is becoming less concentrated. Despite the declining trend, most of the power dissipated by tornadoes remains highly concentrated on relatively few days.
1 Introduction Tornadoes are among the deadliest severe convective weather hazards in the USA. They caused a total of 19,452 fatalities from 1808 to 2017 (Agee and Taylor 2019). The number of fatalities per year was stable across the early-to-mid decades within this period (e.g., 1880–1949) but has declined across the most recent decades (e.g., 1950–2005) (Ashley 2007; Fricker et al. 2017). Despite this decline, tornadoes are still a notable hazard, as they were responsible for an average of 69 deaths per year over the most recent 10 years of record, 2009– 2018 (NWS 2019). The number of fatalities and injuries (i.e., casualties) a tornado produces depends on complex interactions between the geophysical attributes of the tornado, the socioeconomics and demographics of the affected population, and the built environment (Boruff et al. 2003; Merrell et al. 2005; Ashley 2007; Ashley et al. 2008; Sutter and Simmons 2010; Simmons and Sutter 2011; Dixon and Moore 2012; Ashley and Strader 2016; Strader et al. 2016, 2017a and b; Fricker et al. 2017; Elsner et al. * Todd W. Moore [email protected] 1
Department of Geosciences, Fort Hays State University, Hays, KS, USA
2
School of Sciences, University of Louisiana Monroe, Monroe, LA, USA
2018; Strader and Ashley 2018). Important geophysical attributes include the estimated intensity and energy dissipation, or power, of a tornado. Tornadoes with higher damage ratings (e.g., strong and violent (E)F2–(E)F5) yield more casualties than do tornadoes with lower ratings (e.g., weak (E)F0–(E)F1) (Merrell et al. 2005; Ashley 2007; Simmons and Sutter 2011). Tornadoes that dissipate more energy (i.e., those with greater power) also tend to yield greater casualty counts (Fricker et al. 2017; Elsner et al. 2018; Fricker and Elsner 2019). The number of casualties is also positively related with tornado outbreak metrics (Fuhrmann et al. 2014), meaning that casualty counts tend to be greater with outbreaks of more t
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